MORPHOLOGY:
The red howler monkey has a prehensile tail without hair on the bottom side, which is used for grasping during locomotion and feeding. The upper molars have sharp shearing crests, which are used in grinding leaves. The hyoid bone is modified for the production of the howling calls indicative of members of this genus; this bone is larger in males than in females. This species is sexually dimorphic in terms of size (Fleagle, 1988). The average body mass for males is between 6 and 8 kilograms, and for females it is between 4.5 to 5.5 kilograms.

RANGE:
The red howler monkey is found in the countries of Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Peru, Suriname, and Venezuela. This species lives in secondary, gallery, swamp, and savanna forest habitats.

ECOLOGY:
The red howler monkey consumes new leaves and fruit as the main part of the diet. Flowers and insects are also sometimes eaten. This species, along with other members of its genus, have large salivary glands that help to break down the tannins in the leaves before they reach the gut (Milton, 1987). This is a diurnal species. The group size for this species is between 3 to 16 individuals (Crockett and Eisenberg, 1987). Both males and females disperse from natal groups in this species.

LOCOMOTION:
The red howler monkey moves slowly through the forest using a quadrupedal mode of locomotion (Fleagle, 1988). This species uses its tail to suspend from branches while feeding (Fleagle, 1988).

SOCIAL BEHAVIOR:
The groups of red howler monkeys come in two kinds: one, a group of one or two males, a few females, and their offspring and two, a group of bachelor males. Members of the bachelor male troops will fight with the male in charge of the females to try to take over the troop (Fleagle, 1988). Other females than the mother will care for the infants (Fleagle, 1988). This species rarely performs allogrooming, and if done is usually performed by adult females (Kinzey, 1997). Infanticide has been reported for this species where it is a major cause of infant mortality (Crockett and Rudran, 1987).

VOCAL COMMUNICATION:long call: This call is amplified by the hyoid bone which acts as a resonator, and the calls travel for long distances (Kinzey, 1997). The calls serve to communicate group location, distance, and composition, and the calls are directed at solitary individuals and/or other members of the group (Kinzey, 1997). These calls are most often heard at dawn (Kinzey, 1997).

OLFACTORY COMMUNICATION:

VISUAL COMMUNICATION:

TACTILE COMMUNICATION:

REPRODUCTION:
The red howler monkey gives birth to a single offspring.